Phenom's largest gains may well come from applications which make full use of all 4 cores, as the single L3 cache will help keep the cores flowing.
On single threaded applications, they will be relying on other improvements, like the rumoured twin FPU's per core. But that depends on what the program needs. Im guessing there will be benchy's which show the Phenom to be very fast, and others showing Core 2 is still very good. In the real world.. who knows Perhaps Phenom will be fastest, or Perhaps it will be Core2.. Or it could be so close, that its impossible to call it.
We'll only know for sure when the production chips are out. But I hope for AMD that they already have the next chip's ready to go to test silicon.. Intel are far down the road towards Nehelem, and are probably already working on the next chip after that as well.
It seems likely that AMD and Intel will now alternate as to who has the fastest chip at any given 'stock' speed, but Intel wont just sit back on a single core design, trying to make a single design 'work'. P4 should have been scrapped years ago, but they continued to try and fix it, giving AMD a long time ruling the top performance.